test_time.c

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/**
 * @file test_time.c
 * Tests clocks/timekeeping.
 */

#include <px4_platform_common/px4_config.h>
#include <px4_platform_common/defines.h>
#include <px4_platform_common/posix.h>
#include <sys/types.h>

#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <fcntl.h>
#include <errno.h>

#include <arch/board/board.h>

#include "tests_main.h"

#include <math.h>
#include <float.h>
#include <drivers/drv_hrt.h>


static hrt_abstime
cycletime(void)
{
    /* emulate hrt_absolute_time using the cycle counter */
    static uint64_t basetime;
    static uint32_t lasttime;
    uint32_t cycles;

    cycles = *(unsigned long *)0xe0001004;

    if (cycles < lasttime) {
        basetime += 0x100000000ULL;
    }

    lasttime = cycles;

    return (basetime + cycles) / 168;   /* XXX magic number */
}

int test_time(int argc, char *argv[])
{
    hrt_abstime h, c;
    int64_t lowdelta, maxdelta = 0;
    int64_t delta, deltadelta;

    /* enable the cycle counter */
    (*(unsigned long *)0xe000edfc) |= (1 << 24);    /* DEMCR |= DEMCR_TRCENA */
    (*(unsigned long *)0xe0001000) |= 1;        /* DWT_CTRL |= DWT_CYCCNT_ENA */

    /* get an average delta between the two clocks - this should stay roughly the same */
    delta = 0;

    for (unsigned i = 0; i < 100; i++) {
        uint32_t flags = px4_enter_critical_section();

        h = hrt_absolute_time();
        c = cycletime();

        px4_leave_critical_section(flags);

        delta += h - c;
    }

    lowdelta = abs(delta / 100);

    /* loop checking the time */
    for (unsigned i = 0; i < 100; i++) {

        usleep(rand() % SHRT_MAX);

        uint32_t flags = px4_enter_critical_section();

        c = cycletime();
        h = hrt_absolute_time();

        px4_leave_critical_section(flags);

        delta = abs(h - c);
        deltadelta = abs(delta - lowdelta);

        if (deltadelta > maxdelta) {
            maxdelta = deltadelta;
        }

        if (deltadelta > 1000) {
            fprintf(stderr, "h %" PRIu64 " c %" PRIu64 " d %" PRId64 "\n", h, c, delta - lowdelta);
        }
    }

    printf("Maximum jitter %" PRId64 "us\n", maxdelta);

    return 0;
}